1. Field of the Invention
The present invention relates to a device for closing one end of a core barrel installed in equipment used for drilling for minerals or oil.
2. Description of the Prior Art
It is known that a core barrel can be installed at the end of a line of rotating hollow drill-rods used for test drilling, in particular in geological layers containing minerals and oil, said core barrel allowing samples to be taken from these layers, for example for analysis.
This core barrel which may be, for example, of the type described in Belgian Pat. No. 875016 comprises, on the one hand, an external rotating tube which is constituted by drill-rods and of which the lower end bears a welding ring and, on the other hand, an internal, non-rotating tube, the lower end of which is provided with an extracting cone.
In a core barrel of this type, a drilling liquid is injected inside the drill-rods from the surface.
At the beginning of the drilling operation, it is essential to guide the drilling liquid through the core barrel in order to clear and clean the debris which has accumulated at the bottom of the shaft during the rise and fall of the drill-rods.
A core sample which is representative of the ground cannot in fact be taken until the clearing operation is completed.
While cutting out a core sample, the flow of drilling liquid is generally diverted toward the exterior of the core barrel into an annular space surrounding it. This annular space is defined by the internal wall of the lower rod of the set of hollow drill-rods and the external surface of the internal tube of the core barrel.
In known boring or drilling equipment, the flow of drilling liquid is diverted by freely throwing, from the end of the line of drill-rods remote from the core barrel, a ball intended to close a seat provided at the upper end of the core barrel. It is known that the flow of drilling liquid can be increased in order to accelerate the descent of the ball.
In practice, even though the flow of drilling liquid can be as high as 1,500 liters per minute, the descent of the ball in line of hollow drill-rods having a length of approximately 3,000 meters can take about 20 minutes, with a device according to British Pat. No. 2,048,996 which corresponds to U.S. Pat. No. 4,452,322.
In addition, it has been found that, at the end of its drop, the ball abruptly strikes the above-mentioned seat and causes in the descending column of drilling liquid a surge which damages the core barrel and possibly the boring shaft.
This British patent proposes to divert the flow of drill flushing fluid by means of a valve body releasing a ball in the vicinity of the core barrel and closing a seat provided at the upper end of the core barrel.
The valve body is restrained in a releasable storage cavity arranged in the core drill device, in the vicinity of the core barrel by means of a latch consisting of an annular body formed as a piston housing under a preload. The core barrel is connected to the steam path of the drill flushing fluid by an inlet comprising a seat at the upper end of the core barrel. The piston is movable downwards against the preload when the pressure of the drill flushing fluid is increased to a maximal value by the operators of the drilling equipment at the surface.
The piston, provided with a lateral opening, liberates the ball which reaches and closes immediately, but violently, the seat at the inlet of the core sleeve, stops the flow of drill flushing fluid through the core sleeve, and diverts the flow into the annular space between the outer sleeve and the core sleeve.
This boring or drilling apparatus thus has the drawback that the ball, at the end of its drop, under excessive flow velocities abruptly strikes the above-mentioned seat and causes a surge which damages the core barrel and possibly the boring shaft.